Laboratory Director Stewart Prager heralds start of new era with NSTX-U and looks to future projects in “State of the Laboratory” address

The completion of the $94 million National Spherical Torus-Upgrade (NSTX-U) will usher in a decade of research that will lead to vital results for the international and national fusion programs and could lead the way to a next-step fusion facility, Princeton Plasma Physics Laboratory Director Stewart Prager told staff members in his annual “State of the Laboratory” address on Oct. 5.

When research on the facility begins later this year, it will herald the start of a 10-year research program on the apple-shaped device called a “tokamak,” Prager said. Some 300 researchers, two-thirds of them from outside the Laboratory, will conduct research on the device that will advance the effort to create clean, safe, and affordable fusion energy as a source of generating electricity.

“A new era”

NSTX-U is currently “the most capable spherical tokamak in the world, soon to be joined by our sister facility in England, the MAST,” Prager said. “It will be a research anchor for the Laboratory and guarantee the future of the Laboratory for at least a decade. It is truly a national facility. This is where we are. We’re starting a new era.”

Research on the experiment will lead to new discoveries in plasma physics that can be applied to ITER, the international fusion experiment in Cadarache, France, Prager said. NSTX-U research could advance the spherical tokamak as a candidate for a next-step fusion facility. It will also help researchers identify the best materials to serve as a boundary between the super-hot plasma in experiments and the tokamak walls.

“I just want to say congratulations and thank you to the entire NSTX U project team for a momentous accomplishment,” Prager said, as the crowd applauded loudly. “It’s of overwhelming importance to the Laboratory and the future of fusion energy.

Broadening PPPL’s research focus

A next challenge for the Laboratory, Prager said, is to broaden its research focus to include diverse topics, while at the same time contributing to and preparing for a world fusion program through ITER. The Laboratory’s leadership needs to think “with a sense of urgency” about the U.S. fusion program 10 years into the future and about PPPL’s next research program, Prager said. At the same time, PPPL will implement a campus infrastructure program to renew and improve its infrastructure. A $25 million plan of refurbishment is scheduled to begin next summer.

Looking at PPPL’s funding, Prager said he did not know how much PPPL would receive in fiscal year 2016, which began Oct. 1 as we await Congress passing the fiscal year 2016 budget. However, he said the last two years have been fairly stable with $100 million in fiscal year 2015 and $101 million in funding in fiscal year 2014, up from $86 million in 2013.

PPPL’s strategy is aligned with the DOE’s Fusion Energy Sciences Program’s emphasis on burning plasma science, (science aimed at a self-sustaining plasma such as the one that will be produced on the ITER experiment), and discovery science (research that may or may not be directly related to fusion research).

A possible breakthrough solution

One promising direction for the Laboratory in burning plasma science is research into utilizing liquid metals as a kind of protective wall between the plasma, which is heated to temperatures hotter than the sun, and the tokamak wall. “Liquid metal is a possible breakthrough solution,” Prager said. “If you surround the plasma by a liquid, it doesn’t break, it is self-healing, and it can carry heat out if it’s flowing.”

The topic would be “a perfect research topic” for both the United States and the Laboratory, Prager said. PPPL’s Lithium Tokamak Experiment (LTX) and the surface science laboratory have both done important research in this area, he said. A lithium boundary could be tested in NSTX-U. One possible future research project is a full torus with flowing lithium, he said.

PPPL researchers working on the LTX have recently shown that the lithium boundary improves the plasma energy confinement, Prager said. PPPL plans to expand the capabilities of the LTX in the future by adding a neutral beam for core fueling and heating.

Prager noted that lithium is a hazardous material but a recent DOE review gave high marks to the Laboratory for its safe handling of the material.

Computational research increasingly important

Another strategic research area, computational research, has become increasingly important in fusion energy research, Prager said. Researchers use sophisticated computer models along with NSTX-U measurements to shed light on disruptions that can interrupt fusion experiments. They also focus on turbulence in the complex edge region, an important research area in fusion energy research. “We’re learning more and more that to some extent the edge is the dog that wags the tail of the whole tokamak,” Prager said.

Prager noted that the TRANSP code, which was developed at PPPL several years ago, is being used as a research tool in fusion facilities worldwide. In fact, scientists at a recent user-group meeting called for PPPL researchers to enhance the capabilities of the TRANSP code.

PPPL researchers are also focusing on stellarators that could sustain a plasma in steady-state, in keeping with the FES long-pulse research goal. PPPL is leading a team of researchers from U.S. laboratories who collaborate on the Wendelstein 7-X stellarator being constructed in Germany, Prager said. PPPL engineers oversaw the construction of magnetic trim coils and physicists installed an X-ray spectrometer on the device.

PPPL has also made significant contributions to ITER, which will be the focus of international fusion research. “I think in 2080 when we look back at the century, ITER will be viewed as a landmark experiment of the century,” Prager said. PPPL is responsible for the U.S. contribution to diagnostics, and delivered a $42 million steady-state electric network, which powers all of ITER, Prager said. “It was delivered with great technical success and also on time and on schedule,” he said.

Stellarators could play important role

Looking ahead to PPPL’s long-term future, Prager said stellarators could play an important role. “Stellarators are crucial for fusion, an innovative research opportunity for the United States and a possible major component of the Laboratory’s future,” he said.

He noted that a PPPL study group is identifying possible future stellarator paths and developing new ideas on how to optimize the design and simplify magnet shapes. A next step would be to enlarge the study to a national effort, Prager said.

Another concept for a future project at PPPL would be a tokamak that would be surrounded by a liquid-metal wall. “A challenge now is to develop the most compelling future for the major U.S. effort on plasma material interface,” Prager said.

And while a pilot plant or nuclear science facility “is not currently on the table,” Prager said it’s important that researchers explore the scope of such projects. “We continue to advance our understanding to possible aggressive next steps, in concert with other U.S. fusion groups,” he said.

Next generation of MRX

One example of “discovery science” at PPPL is research on the Magnetic Reconnection Experiment (MRX) into magnetic reconnection, the mysterious process responsible for solar flares, geomagnetic storms, star formation and other phenomena throughout the Universe. The next generation reconnection experiment, the Facility for Laboratory Reconnection Experiments (FLARE), is under construction at Princeton University and will be completed by late 2016. Funding for the project comes from the National Science Foundation and the University.

PPPL has begun research into plasma synthesis of nanomaterials. That project is funded by the DOE’s Basic Energy Sciences (BES), establishing a BES/FES partnership, Prager said. A new expanded lab for plasma nanotechnology is being refurbished.

“To conclude, the start of NSTX-U signifies a new research opportunity,” Prager said, “and looking forward to the future, through the creativity of all of you we’re developing new fusion opportunities for the near-term and long-term, small-scale and large-scale.”